"I suppose in retrospect there would be some discussion over what 'any document' meant."

Cardinal Pell said specific requests about cases would be more likely to succeed than what he described as an "ambit claim" for large numbers of documents.

A letter from the royal commission to the Vatican said it needed access to documents if it was to fulfil its terms of references.

"It is essential that the royal commission understand the nature and extent of the communications between those congregations and the Holy See in relation to child sexual abuse complaints about Australian clerics," the letter said.

Cardinal Pell said the Vatican had provided 5000 pages of documents in relation to specific requests.

"But in following international convention they will not provide internal working documents of another sovereign state," he said.

Cardinal Pell said he thought the royal commission's request for documents relating to each case was "unreasonable".

"Overwhelmingly every document that is held in Rome exists here ... I am not aware of exceptions - overwhelmingly they are available in Australia," he said.

A letter from the Vatican's Secretariat of State said finding every file on accused Australian priests would be a substantial burden, "inconsistent with international practice".